The lady's name is Casey Garcia ... a 30-year-old who's got a 7th grader attending Garcia-Enriquez Middle School near El Paso ... whose security process she wanted to test by going "undercover" as a student ... just to see how far she could get without being caught.

Garcia recorded her experience and posted the footage on YouTube, TikTok and other social media platforms -- which have taken off and gone viral. It's pretty crazy ... she does a full incognito attempt, undergoing a makeup routine and a wardrobe change to pull it off.

Sure enough, she does kinda resemble a middle schooler -- granted, the face mask she had to wear certainly helped. Still, she made it through about 85% of the school day undetected.

Garcia is seen walking through the halls, interacting with faculty, sitting in class listening to lectures, and even eating lunch at one point ... and no one seems to notice she's an adult. Eventually, the jig was up ... somebody called her out and reported her to the principal.

She went willingly -- and even though she seemed to think it was NBD ... the administration thought differently, getting the police involved who busted her for falsifying records and for trespassing. The incident happened Tuesday, but she wasn't booked until this past Friday.

Again, the whole point of doing this was to show that the school was a little too lax when it came to vetting students ... especially as kids start heading back to campus in person.

Of course, people were concerned Garcia could get in so easily ... which could pose bigger problems if it was someone who meant to do harm. The superintendent reportedly sent a note to parents saying they were reviewing and revamping their security measures.

If this sounds like something straight out of a movie, that's because it kinda is. Drew Barrymore did something similar in "Never Been Kissed" -- except that was high school.